A continuously variable transmission of this kind is constructed with, e.g., clamping a disc-shaped rollers between a pair of discs arranged opposed to each other. The portion of the pair of discs where is the outer side from a predetermined radius has an arcuate plane congruent with the arc centered on the center points of opposed planes of those discs, and such arcuate planes is leading to circumferential direction. The plane thus incurved three-dimensionally is a toroidal plane. The toroidal plane functions as a rolling face and the rollers is clamped therebetween. The roller is a disc-shaped member and its sectional figure along the in-depth direction of the outer circumferential portion is congruent with the arcuate figure of the rolling face of the discs. Accordingly, the roller is rotated by means of rotating one of the discs, and the other disc rotates sequentially. Then, the roller is inclined to move the radial position of the contact portion against one of the discs, i.e., the radial position from the center axis of the disc outward, and also to move the radial position of the contact portion against the other disc to inner circumferential side, so that the gear ratio corresponding to the proportion of the radii of each contact portions is accordingly set.
Toroidal type continuously variable transmission is categorized into full-toroidal type and half-toroidal type according to the configuration of their toroidal plane. The former mentioned full-toroidal type continuously variable transmission has the toroidal plane on its disc, which is formed to make the clearance between the toroidal planes opposed to each other broader outwards in the radius direction gradually, and then to make the clearance narrower gradually. On the other hand, latter mentioned half-toroidal type continuously variable transmission has a toroidal plane on its disc whose configuration is half shape of said full-toroidal type, and the clearance between the toroidal faces opposed to each other is widest at the outer circumferential side of the discs.
In any of those types of continuously variable transmissions, roller is clamped between a pair of discs, and the pressure is set with corresponding to the torque to be transmitted. Also, the contact face of the disc and the roller with an oil film being interposed therebetween is not flat a plane, therefore, the load to change the posture acts on the roller. For example, in the former mentioned full-toroydal type continuously variable transmission, the load for inclining the rollers is generated in connection with the movement of the roller backward and forward by means of supporting the roller with so-called caster angle. On the contrary, in the half-toroidal type continuously variable transmission, because the rolling face of the disc open to outer circumferential side, the thrust load for pressing the roller outwardly in a radial direction is generated by clamping the roller with the discs.
In this connection, full-toroidal type continuously variable transmission is constructed to execute the speed change with utilizing the load which acts to incline the aforementioned roller. One example of such is disclosed in Japanese Patent Laid-Open No. 10-132047. To describe specifically, a roller clamped between a pair of discs is held by a support member in a rotatable condition, and the support member is connected to a piston rod of a hydraulic cylinder. The hydraulic cylinder is arranged with being inclined in a horizontal direction in order to set the predetermined caster angle to the vertical plane against the center axis of the discs.
Accordingly, the roller is moved between the discs backward and forward in connection with the movement of a piston rod of the hydraulic cylinder backward and forward, so that the roller is inclined against the center axis of the discs with corresponding to its anteroposterior position. Consequently, the position of the contact portion of the roller against the input disc in the radius direction and the position of the contact portion of the roller against the output discs are differed each other; therefore, the gear ratio which corresponds to the proportion of distance between those contact portion and the center axis of the discs is accordingly set.
In the full-toroydal type continuously variable transmission, as mentioned above, an actuator such as a hydraulic cylinder for executing speed change by means of moving the roller backward and forward is arranged with leading to the direction having a predetermined angle of inclination against the plane vertical to the center axis of the discs, from between the input disc and the output disc. On the other hand, the input disc and the output disc are arranged collinearly and the roller is clamped between those discs, so that the housing space for the discs and the roller may be cylindrical space.
Thus, the way of arrangement of discs and rollers, and the way of arrangement of the actuators for moving the rollers forward and backward are different; and moreover, a plurality of rollers is arranged in the circumferential direction of the discs with keeping constant distance; so that a plurality of actuators has to be arranged with protruding from arrangement space for the discs and so on in the radius direction.
In order to support such actuators, for instance, it is considerable to form a plurality of cylindrical shaped protrusion on the outer circumferential wall portion of the housing of continuously variable transmission, and to accommodate actuators in such protrusions. However, if it is constructed as such and employed as a speed change device for a vehicle, mountability becomes worse because the structure has to be complicated due to big convexes and concaves, and the requirement for down sizing and weight saving cannot be fulfilled accordingly. Moreover, productivity also becomes worse because a plurality of core and sand cast have to be employed for casting a housing. Furthermore, the specifications such as length of oil passages and so on have to be unified when the oil pressure is fed to each actuators, because rollers arranged in the circumferential direction with keeping constant distance have to exhibit the identical behavior simultaneously to execute speed change. However, in the aforementioned structure in which a plurality of actuators is held with being protruded from the housing in the radius direction, the structure of piping to the actuators becomes complicated. Consequently, there are disadvantages such as lag in the action timing between individual actuator and so on.
This invention has been conceived noting the aforementioned technical problem and has an object to provide a toroidal type continuously variable transmission which can simplify its outer shape and the arrangement of oil passages for lubrication oil and hydraulic for control.